We used to run our young colts and gelding together in a large pasture. The younger stallions generally stayed in the group until they had their first season at stud. So they all grew up in a herd situation. Currently, we don't have many, and my gut feeling is that not all the older (breeding) stallions would be ok with it.
But we do have one established and working mini-bachelor herd. Max (American Saddlebred, 16 years old) shares his paddock happily with Serrano (Paso Creole, 3 years old). I think it's great for both of them and I'm hoping it will still work after Serrano is introduced to the ladies, maybe in the season after this one (aged 4+). But we'll see.
I have often been tempted to try out some of the other ones together. We've had the odd whoopsie with the electric fences and they ended up together anyway. Yes, there is a lot of noise, but aside from a few minor scrapes, it never led to anything. They are all housed in small paddocks separated by 6 meter laneways, so they well know each other.
It is interesting to read that someone has done some research into the behaviour of grouped stallions in domestic breeds. A Swiss study titled "Pattern of Social Interactions after Group Integration: A Possibility to Keep Stallions in Group" makes for interesting reading. The complete journal article can be read on PLOS|One.